Lifetimes of nuclear excited states with neutron gated recoil distance method

A motor driven plunger has been constructed for measuring lifetimes of nuclear excited states in pico second region. An array consisting of six neutron detectors was used to clean up γ-spectra obtained with CS-HPGe detectors. Lifetimes of low excited states in neutron deficient nuclei with low production cross-section e.g.⁸¹Y,⁷⁷Kr and⁷⁸Rb are reported.     

A new approach to stroboscopic resonance measurements of the nuclear quadrupole interaction

A new stroboscopic resonance method for the measurement of the quadrupole interaction of long-lived nuclear isomers excited by pulsed beams with a fixed repetition frequency is demonstrated. The method utilizes the phenomenon of beats which occurs when a magnetic perturbation is introduced in the presence of a pure quadrupole interaction. The nuclear precession is thus controlled by the beat frequencies which can be varied by the external magnetic field which is oriented parallel to the symmetry axis of the crystal. Stroboscopic resonance can be achieved by varying thebeat frequency to be an integral multiple of the beam pulsing frequency. The method is demonstrated using the 398 keV level of⁶⁹Ge excited and recoil implanted into a single crystal of tin by means of a heavyion reaction.Supported in part by the National Science Foundation.     

Searches for effects of fundamental-symmetry violation in isomeric nuclear states

The results of broad searches for schemes that are convenient for observing effects of time-inversion-invariance violation (T violation) simultaneously with parity violation (PT violation) in electromagnetic transitions in nuclei are presented. The main problems in observing such effects are discussed. A scheme that seems one of the most promising for this and which relies on measuring the linear polarization of gamma radiation accompanying the deexcitation of isomeric states of nuclei that were oriented by a magnetic field at ultralow temperatures is highlighted.     

A modified stroboscopic method for non-linear vibration equations

A technique is developed for determining approximate periodic solutions to a class of non-linear differential equations which often arise in vibration theory. Although it is akin to the stroboscopic method of Minorsky, no topological arguments are utilized. The method is illustrated by application to a well known example and it is shown to give correct results.     

g factor measurements of high spin isomeric states in 187,189,191 Au

The g factors of three high spin isomers in ^187,189,191Au have been measured, using the time differential perturbed angular distributions. The reactions used and the results obtained for the g factors and the lifetimes are: ¹⁷²Yb(¹⁹F, 4nγ) ¹⁸⁷Au, g (31/2- or 35/2-) = 0.25 (3), T_1/2 = 102 (5) ns; ¹⁸¹Ta ( ¹²C, 4nγ) ¹⁸⁹Au, g (31/2+) = 0.42 (2), T_1/2 = 242 (10) ns; and ¹⁷⁶Yb(¹⁹F, 4nγ) ¹⁹¹Au, g (31/2+) = 0.42 (3) T^1/2 = 402 (20) ns. These results show that the structure of these isomers is consistent with a 1 proton, 2 neutrons structure. The experimental set-up was cheked by measuring the g factor of the Coulomb excited 197 keV, T_1/2 = 89.3 ns level of the ¹⁹F beam stopped in the lead backing.     

Influence of high-spin states on isomeric ratios of nuclear reaction products

The isomeric ratios of some nuclear products of (p, n), (d, 2n), (α, p3n) reactions were analyzed. A comparison of calculation data obtained by using TALYS 1.4 software package with experimental ones shows that the observed significant discrepancies for definite nuclei may be accounted for by the influence of high-spin states on the values of isomeric ratios.     

In-beam measurements of magnetic moments of excited nuclear states

In-beam measurements of magnetic moments of very short-lived nuclear states employing the transient field technique are presented. Particular features of this experimental method relevant for its successful application are discussed. Instead of surveying a large body of data significant details of the capacity of this technique are demonstrated by giving preference to a few selected examples. Particular emphasis is put on high-spin states of deformed nuclei whose structure is dominated by rotationally-aligned single particle configurations.     

Effect of nuclear-reaction mechanisms on the population of excited nuclear states and isomeric ratios

Experimental data on the cross sections for channels of fusion and transfer reactions induced by beams of radioactive halo nuclei and clustered and stable loosely bound nuclei were analyzed, and the results of this analysis were summarized. The interplay of the excitation of single-particle states in reaction-product nuclei and direct reaction channels was established for transfer reactions. Respective experiments were performed in stable (⁶Li) and radioactive (⁶Не) beams of the DRIBs accelerator complex at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, and in deuteron and ³Не beams of the U-120M cyclotron at the Nuclear Physics Institute, Academy Sciences of Czech Republic (?e? and Prague, Czech Republic). Data on subbarrier and near-barrier fusion reactions involving clustered and loosely bound light nuclei (⁶Li and ³He) can be described quite reliably within simple evaporation models with allowance for different reaction Q-values and couple channels. In reactions involving halo nuclei, their structure manifests itself most strongly in the region of energies below the Coulomb barrier. Neutron transfer occurs with a high probability in the interactions of all loosely bound nuclei with light and heavy stable nuclei at positive Q-values. The cross sections for such reactions and the respective isomeric ratios differ drastically for nucleon stripping and nucleon pickup mechanisms. This is due to the difference in the population probabilities for excited single-particle states.     

Half-life measurements of 137, 139Cs excited nuclear states

A fast-timing setup has been developed to measure the nuclear-state half-lives of neutron-rich nuclei. The first on-line measurements were performed on ^{137, 139}Cs obtained from the β decay of ^{137, 139}Xe. These neutron-rich Xe nuclei were produced by the ²³⁸U photofission induced by the 50MeV electron beam delivered by the ALTO facility. The half-lives of the first excited state in ¹³⁷Cs and of six excited states in ¹³⁹Cs were measured for the first time. Taking into account new information given by the deduced transition probabilities, we discuss the structure of the first excited states in ^{137, 139}Cs : it is shown that, in both nuclei, the first excited $\tfrac{5} {2}^ +$ level corresponds mainly to the one-proton state issued from the π2d _5/2 orbital and that the most probable spin values for the states located at 289.8, 393.5, and 393.8keV in ¹³⁹Cs are $\tfrac{5} {2}^ +$ , $\tfrac{3} {2}^ +$ , and $\tfrac{1} {2}^ +$ , respectively.     

Double-frequency stroboscopic method for absolute calibration of vibration transducers

This paper describes a new stroboscopic technique for a more accurate optical determination of vibration amplitude for the purpose of calibrating vibration transducers; the apparatus is composed of standard equipment which has been adapted to purpose-developed circuitry.     

Search for high-spin isomeric states in the rare-earth region

Several new high-spin (I>10) isomeric states in the mass region A=144–164 are located in a systematic search with ¹²C induced reactions, employing a sixteen NaI (Tl)Ge(Li) detector multiplicity filter. The proximity to the N=82 neutron shell closure strongly suggests that shell effects contribute significantly to this isomerism.     

Observation of isomeric states in197Bi

The high spin states of¹¹⁹Te, populated in¹¹⁰Pd(¹³C,4n) and¹¹⁰Pd(¹²C,3n) reactions, have been studied through -ray spectroscopy. The level scheme has been established upto a spin of 55/2. Three-quasiparticle states, based on g² _7/2h_11/2 and g_7/2d_5/2h_11/2 configurations, have been identified. The 35/2 and 39/2 states are suggested to be the fully aligned states constituted by five valence h_11/2 ³, g_7/2, d_5/2 quasiparticles.     

Further reduction of recording time in stroboscopic holographic interferometry

Except for the extreme positions, a vibrating object passes twice through a position in each vibration cycle. It is suggested that this fact can be used to reduce the recording time during the pulsed illumination in stroboscopic holographic interferometry by providing two light pulses per vibration cycle for a given subject position.     

Spontaneous fission of isomeric states of actinide nuclei

Spontaneous fission half-lives of K-isomeric states are calculated on the basis of microscopic- macroscopic method. The isomeric state is assumed to be a 2-quasiparticle excited state with high angular momentum.The calculations were performed for nuclei with 96 < Z < 110 and 144 < N < 158. It was shown that in the case of K-isomeric states (if they exist) the spontaneous fission half-life time may be comparable to the spontaneous fission half-life time of the ground state. Therefore it was suggested that in measurements of fission half-lives it may be very important to distinguish between both possible components (or more) of the fission decay.     

Generation of long-lived isomeric states via bremsstrahlung irradiation

A method to generate long-lived isomeric states effectively for Mössbauer applications is reported. We demonstrate that this method is better and easier to provide highly sensitive Mössbauer effect of long-lived isomers (>1 ms) such as ¹⁰³Rh. Excitation of (γ,γ) process by synchrotron radiation is painful due mainly to their limited linewidth. Instead, (γ,γ’) process of bremsstrahlung excitation is applied to create these long-lived isomers. Isomers of ⁴⁵Sc, ¹⁰⁷Ag, ¹⁰⁹Ag, and ¹⁰³Rh have been generated from this method. Among them, ¹⁰³Rh is the only one that we have obtained the gravitational effect at room temperature.     

An exotic type of nuclear isomeric transition

A new type of nuclear isomeric transition similar to double beta decay, the β^-? process, is proposed. Under the full ionization of atoms, this process can compete with ordinary types of nuclear isomeric transitions in which the excited metastable state is deexcited via a gamma transition.